Can Humans Hibernate? Ask the Dwarf Lemur

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Sheena L. Faherty is a Ph.D. candidate in the Biology Department at Duke University. She blogs about her field experiences in Madagascar at Musing of a Jungle Queen, where she provides a unique, first-hand account of the challenges and incredible experiences of life in the field, especially for a self-described “clumsy hiker”. Follow on Twitter @junglequeen18.

After a teenage stowaway flew from California to Hawaii hidden in the wheel well of an airplane this week, investigators immediately began to wonder how he had survived the freezing temperatures and low-oxygen conditions of the unpressurized compartment.

The fat-tailed dwarf lemur (Cheirogaleus medius) is the only known primate hibernator and can only be found on the island of Madagascar (Credit: David Haring, Duke Lemur Center)

How do I know this? Well, I study the closest genetic relative of humans known to hibernate. The only primate to do so, the dwarf lemur of Madagascar spends up to eight months of the year in hibernation—an astounding feat, especially for a primate.

Hibernation is an extreme survival tactic that some mammals living in seasonal environments use when resources disappear and threaten overwinter survival. This radical deviation from normal physiology involves a whole gamut of bodily systems gone haywire: heart rate is nearly arrested, body temperature plummets to near or below freezing levels, and brain activity virtually ceases. Hibernating animals look dead.

Almost.

The heart rate of an active dwarf lemur is around 180 beats per minute, but during hibernation it can drop to as low as four beats per minute. Body temperature, which usually hovers around 36 degrees Celsius, can plunge to almost freezing at a frigid 5 degrees C. And I’ve recently witnessed a hibernating dwarf lemur go 21 minutes without taking a breath. (Warning: Don’t try this, unless you happen to be holed up in a wheel well of an airplane).

Many of the physiological changes that happen during hibernation would be fatal to non-hibernating species. Yet dwarf lemurs master these changes successfully during the hibernation season, year after year after year.

This gloriously weird physiology is displayed in an animal that shares about 97 percent of our genome. But here’s punch line #1: As the Hawaii stowaway demonstrated, humans might already have the mechanisms that confer the ability to hibernate present in our genome.

Hibernation biologists now believe these extreme modifications of normal physiology are due to underlying changes in gene expression. Think of this as analogous to a very sophisticated light bulb. This light bulb requires multiple switches to be flipped on for light emission, and only the correct combination of switches will suffice. The light bulb in this example is the hibernation response (i.e. if it’s lit up the animal is hibernating) and the light switches are the genes involved.

To put it in the context of dwarf lemur hibernation, here is an example: Preceding hibernation, dwarf lemurs get fat. Excessively fat. As fat as they can manage given the food resources available, sometimes more than doubling their body weight all in a matter of little over a month. And they store this fat in their tails.

During the rainy season, their habitat is replete with food and the animals are gorging themselves on fruit and insects—normal carbohydrate metabolism chugging away. Those genes that drive carbohydrate metabolism are flipped on. Then the extreme dry season hits and resources disappear. Dwarf lemurs enter hibernation and since they can only rely on stored fat in their tails to keep the critical physiological processes running, the combination of genes that govern fat metabolism flip on. This leads to a breakdown of fat reserves, which fuels the body during a time of fasting.

In the early 1990s, scientists investigating biochemical changes during hibernation in ground squirrels—a model laboratory hibernating species—documented the first gene exhibiting differences in expression levels between ground squirrels’ active state and when the animals were deep in hibernation. This gene, α2-Macroglobulin (α2M), which functions to inhibit blood clotting, displays higher levels of expression when an animal is hibernating relative to the animal’s active state. This is especially important for survival during hibernation as circulation is nearly arrested due to a reduction in heart rate, increasing the potential risk for fatal blood clots to form when circulation slows down.

This animal demonstrates how lean an animal can get when relying only on stored fat in the tail during the 8 months of hibernation. (Credit: David Haring, Duke Lemur Center)

Remember back in chemistry class when you learned that the lower the temperature, the slower the reaction time would be? Well, when core body temperature is lowered to a few degrees above freezing during hibernation, it follows that fundamental cellular and physiological processes would slow down in response. Punch line #2: They don’t!

The discovery that specific genes, like α2M, are increased in expression during hibernation instead of being decreased as expected means that cellular reactions are still happening despite chilly body temps. This indicates that these molecules must be important for survival during hibernation. Differentially expressed genes could provide vital clues to metabolic functions that are imperative for survival during hibernation, such as fueling a hibernating animal solely through lipid metabolism.

With next-generation sequencing technologies to scan the entire genome for the changes in gene expression that correlate with “physiology gone haywire,” hibernation biologists can compare across the hibernating species and see if similar genes and genetic pathways are responding. Punch line #3: Similar patterns are seen in ground squirrels, black bears and little brown bats—hibernating species that represent a wide-range of the mammalian family tree.

The dry season in Madagascar (Credit: Peter Klopfer, Duke University)

While we don’t know if these patterns hold true for all hibernators, comparable findings in very distantly related mammal species suggest that all mammals, including humans, might already hold the genes needed for hibernation. The next step is to look at the genetic mechanisms regulating dwarf lemur hibernation, our closest hibernating cousin.

Further investigations using animal models (like dwarf lemurs that can survive extreme physiological changes during hibernation) may lead to breakthrough medical treatments to improve the human condition.

For example, understanding the mechanisms of how peripheral tissues withstand insufficient blood flow during hibernation might lead to better technologies for protecting the brain during a stroke or some form of trauma. By figuring out the ways in which hibernating animals avoid atrophy after not using their muscles during eight months of hibernation, researchers might better the lives of immobilized or bed-ridden humans. Dissecting how animals in hibernation can rely solely on stored fat as fuel will indeed have immediate benefits for understanding obesity and other metabolic disorders.

Lastly (and most excitingly for science fiction nerds like myself), figuring out ways to induce humans into a hibernation-like state might make it possible to launch humans into far-flung galaxies, as glorified in popular sci-fi movies like Alien and Prometheus.

When it comes to air travel here on Earth, however, an economy-class ticket is still the best way to go.

About the Author: Sheena L. Faherty is a Ph.D. candidate in the Biology Department at Duke University. She blogs about her field experiences in Madagascar at Musing of a Jungle Queen, where she provides a unique, first-hand account of the challenges and incredible experiences of life in the field, especially for a self-described “clumsy hiker”. Follow on Twitter @junglequeen18.

Is there _any_ confirmed evidence of human hibernation? The referenced news story merely states:
“To have survived the flight, the boy’s body would have had to fall into a hibernation-like state, with his heart beating only a couple of times a minute, said ABC News’ chief health and medical editor, Dr. Richard Besser”
- Unless there is – this is merely wildly speculative conjecture.

Yes, there is a hibernation-like state humans sometimes fall into during cold-water drowning, called the “mammalian response”. This is why you should do CPR on a drowning victim even after a half hour under water if they drowned in cold water. If the victim is lucky enough to have fallen into this state, they can be revived after a half hour under water with no brain damage. Someone who does not fall into this hibernation-like state will die in about 4 minutes, if memory serves. It makes sense the conditions in the wheel well of the plane would have mimicked cold-water drowning (low oxygen & cold body temperature).

Becky is right. I have studied this phenomenon as part of training in giving first aid and if the victim is able to breathe just a little he may survive quite a long time in this state. Breathing under water is impossible of course but I personally know a man who suffered a severe accident and survived in a semi hibernation state for several hours during which time he should have died from his extensive injuries any way due to internal bleeding.

He was felling timber alone and was struck by a tree and knocked unconscious into a shallow stream in January in Virginia when the temperature of the air and water would have been just about at the freezing point. His coworkers found him mostly submerged but face up out of the water after an estimated two hours and it took another couple of hours to get him out of the woods and on the way to a hospital for four hours without treatment.

He survived without any mental impairment but he never fully recovered from some badly broken bones.

I can’t remember where I read it but it was apparently a common strategy in medieval times for starving peasants to all go to bed together with such coverings as they had and stay there almost all the time during bad winters when they had very little to eat.

Some people have suggested that they were able to enter a state that could be described as mild form of hibernation or similar to hibernation in that their metabolisms slowed down enough to enable them to avoid starvation.

I am unable to say whether this is a true account or not but it sounds reasonable at first glance.

I am a farmer by profession and if there is no livestock to be fed and otherwise looked after there is essentially no work to be done outdoors in the depth of winter that can’t be postponed if necessary in a subsistence farming situation.

It is a well established fact that the less you move around the fewer calories you need.Staying in bed with the family would greatly reduce the need for calories to stay warm and also reduce the need for firewood substantially as well.This strategy might well enable some people to survive a tough winter without starving.

There is little doubt we possess many genes that could be expressed under certain circumstances which are little known or entirely unknown.

One of my grandfathers was so hairy that it probably caused him some discomfort in the summer but on the other hand all that hair undoubtedly kept him warmer in the winter too.

I would not be surprised if a few such exceptionally hairy men and women were thrown together and kept together for a few generations in very cold environment their descendants would be hairy indeed.

We can make things along these lines happen in one man’s working lifetime with domestic animals by selective breeding without resorting to any new genetic technologies at all.

The Mammalian Response also known as Diving Reflex apparently relies on cold and pressure stimulation of the facial trigeminal nerves resulting in the total incapacity of the victim. In an emergency this is brought on by the tongue suddenly inflating itself across the back of the throat area thereby stopping all air (and thereby the killing water) entering the body cavity. Like the hibernating lemurs in this study by the jungle queen they soon appear for all intense and purposes to be really dead.

A successful resuscitation method was developed by a Prof. Conn at a Toronto hospital in the sixties which entailed slowly re-warming the blood of those children found trapped under the ice after many hours. This connects to the present day work of Dr. Sam Parnia who has resuscitated many ‘dead’ people up to 6 hours after their heart attack demise using a similar method.

And then this is all associated with the findings of Prof. Richard Johnson who discovered the role of fructose in initializing the Metabolic Syndrome in humans that leads onto obesity. In his recent book ‘The Fat Switch’ he presents the idea that MS is actually natural in most mammals who are preparing for hibernation which is all tied up with uric acid production and friut consumption. Thus his prediction that using ‘allopurinol’ a 50 year old drug used to treat gout possibly will reverse the hibernation progression. Using 900mg a day and fasting for 20 days seems to have got rid of my diabetes plus 20 kg.

The boy in the wheel well was found walking on the tarmac. Either he possibly ‘hibernated’ using Diving Reflex or went into a torpor like state which allows for easier recovery though flying into the warm air of Hawaiian might have had the same effect as doctor’s Conns and Parnia’s methods especially if he is a natural “torpidator”.

“It’s probably fairly well known in some medical circles that crib/cot death is possibly caused by the tongue acting as a valve in the process of ‘diving reflex’. This reflex is apparently used by sea mammals when deep diving to protect the animal from high pressured water entering the body cavity when they open their mouths to catch prey and is activated by pressure and cold on the trigeminal nerves located on their face. This possibly explains why the tongue is the strongest muscle in a mammal’s body. Unfortunately it appears that the SIDS child is suffocated by their own tongue which then relaxes leaving no evidence except the body of a suffocated child. Therefore SIDS could be classed as a ‘cold air drowning’.

Over the years many parents have been found guilty of the murder of their child because of the evidence of suffocation. If the child survives a SIDS encounter then it’s possible there will be brain damage similar to cerebral dysgenesis which is usually a symptom of Autism. Apparently the incidence of SIDS has been reduced by putting children down to sleep on their back, a practice that probably also helps reduce the number of ASD victims. The amount of government funded research grants allotted and money received by fund raisers like ‘Red Nose Day’ charities is probably a nice little earner for the select few still supposedly busy looking for the cause of SIDS.”

One unanswered question for those who want to use hibernation in space travel: do hibernating species live any longer than their non-hibernating relatives? So far as I can tell, hibernation works fine if you’re trying to survive an otherwise lethal season, but I don’t know if it lets you live longer otherwise.

A second question: I thought dwarf lemurs aestivated? What’s this about their body temperature dropping to 5oC? What happens in the wild? Do they hibernate at effectively room temperature?

It seems to me, a number of questions have to be answered before any attempt is made to promote some imagined evolutionary link between the hibernation ability of the dwarf lemur and an inferred ability in humans even given the occasional incident of “mammalian response.”

Here is another horror story:
Paraglider pilot Ewa Wisnerska was sucked 32,000 feet (10km) into the air by the storm cloud during paragliding competition. It happened in Manilla, New South Wales, Australia in 2007. She lost consciousness at some point and regained it almost an hour later when her height decreased to 23000 feet (7km). She landed safely 40 miles from her launch, suffering frostbite to her face and with ice inside her lightweight flying suit — but otherwise unharmed. The exact amount of time she was unconscious is unknown, but her flight track including height was recorded by GPS logger (standard equipment for paragliding competitions)
Full story is here:http://www.telegraph.co.uk/news/worldnews/1542962/Paraglider-survived-in-storm-at-32000-ft.html

If this theory is to be taken as truth, it would be an amazing discovery since there are so many possibilities with this knowledge in the world of science. It seems very plausible to me that humans can hibernate. People that practise intense meditation are able to reach a hibernation-like state.

Hibernation in humans could present an extraordinary use in the world of medicine and healing. A study concerning black bears has shown that wounds heal well during their hibernation state leaving hardly any scars and without any infections. If the genes that cause hibernation can be found in humans and hence be activated the human body could get a real chance at regenerating itself by healing slower and therefore more effectively after it has sustained some serious injuries. I think it poses a much greater advantage over an induced coma.

Torpor in humans subjected to low temperature was studied in USSR by Soviet military scientists, who had much less ethical concerns than the current ones. Rationale was mundane: how soldiers can best survive outdoor mishaps in Russian winter.

Interested readers should find some information about it. But I doubt if this turned to be harmless and controllable – given that no such induced torpor is practised in Russia today.

i think that it is possible for humans to have the hybernation gene because clearly if we evolved from the ape and share so mach of our genetic make up with them then clearly we should. Humans have just addapted to an easier way of life and therefore have lost many of there natural instincts, cave men for instance displayed many more natural insticts than the modern human does

The possibility of humans hibernating is a topic I think anyone will be interested in. If it is truly possible, it will definitely have an impact on the medical field. We will be able to deal with many conditions and in a world of poverty one can imagine the impact.

Although we share 97% of our DNA with the dwarf lemur, the remaining 3% is still a huge difference taking in consideration the complexity of the human genome. Humans are also the only species created to be able to change their environment and thus the question remains if it is really necessary for humans to hibernate. Also, will all of us be able to hibernate or is the gene more exclusive?

I believe that there is evidence of humans found in hibernation-like conditions but I don’t believe that it can be seen as complete hibernation. I fully support research in this field as long as we realize the risks involved.

I think we will all be happy to hibernate for a few months and get rid of our excess fat, though!